This invention relates to an internal-combustion engine having two cylinder banks inclined with respect to the vertical line and, more particularly, to an engine of this type having an oil return system.
Internal-combustion engines having inclined cylinder banks are known in numerous constructions and embodiments and are designed, for example, as V-engines or horizontally opposed engines. An internal-combustion engine of this type is known, for example, from European Patent Document EP 399 216 B1. In the case of this internal-combustion engine, the two overhead camshafts arranged in the cylinder head are driven by an intermediate shaft by way of one timing chain respectively. This intermediate shaft, in turn, is connected with the crankshaft by way of a short chain drive. In this case, the two timing chains are each guided in a timing case by way of which the cylinder head and the crankshaft case are connected with one another. In the driving operation of the motor vehicle, fluctuations of the oil level occur particularly during acceleration, deceleration and cornering. In an extreme case, this may result in one of the two cylinder heads almost completely filling with oil, by way of the connection between the crankshaft case and the cylinder head, while the other runs dry.
From German Patent Document DE 40 07 939 C1, a device is known for returning lubricating oil from a timing space of a cylinder head of an internal-combustion engine. In this case, a lubricant pump is mounted on the cylinder head and is connected on the suction side with a collector and whose delivery pipe is arranged outside the engine section and leads to the oil reservoir. The suction-side collector is also mounted on the outside of the cylinder head housing and is connected with the interior of the cylinder head via bores which are each arranged between two cylinders. The only purpose of this lubricating device is to return the lubricating oil flowing out of the bearings of the camshaft.
It is an object of the present invention to compensate for fluctuations of the oil level of an internal-combustion engine, particularly to avoid an excessive rising or falling of the oil level in the cylinder head during acceleration, deceleration and/or cornering.
This object has been achieved according to the present invention by providing an oil return system which returns oil from each cylinder head to an oil reservoir. One lubricant pump is provided for each cylinder head which takes in oil from the cylinder head and pumps it back into the common oil reservoir, compensating for operationally caused fluctuations of the oil level in the cylinder heads. The oil is therefore pumped back against the effect of the acceleration forces or the centrifugal forces. By arranging the lubricant pumps directly on the cylinder head and by driving them via the camshaft, a continuous operation of the lubricant pumps is ensured in a simple, low-cost manner which is advantageous with respect to mounting. The lubricant pumps therefore do not require any activating sensory mechanism and high-expenditure control devices or high-expenditure drives.
The respective arrangement of the lubricant pump on the exterior wall of the cylinder head results in easy mounting and exchange, as required. Furthermore, according to this arrangement of the lubricant pumps, the space in the interior of the cylinder head is kept free of disturbing influences.
A delivery-side oil-air separating element effectively prevents the oil from foaming. This oil-air separating element may be constructed, for example, as a splash baffle or as a so-called swirl pot.
Advantageously, this oil-air separating element may be housed in the interior of the crankshaft case so that the outer dimensions of the engine will not be increased. Particularly in the case of engines in a horizontally opposed arrangement, the housing in the crankshaft case easily provides for minimize space requirements.
The suction action of the lubricant pump is particularly good if the suction pipe does not exceed a defined length. It is therefore advantageous to arrange the suction pipe in the area of the front wall on which the lubricant pump is mounted, leading directly into the cylinder head. In this case, the suction pipe may extend as a cast or bored duct in the wall of the cylinder head housing.
An advantageous connection pattern for the lubricant pump is obtained when the suction pipe is arranged at least partially in the cylinder head cover. In view of the connection pattern and the overall size, the construction of the lubricant pump as an internal gear pump is advantageous. This internal gear pump may have a relatively compact construction so that the outer dimensions of the overall engine will be only insignificantly changed by means of the mounted pump.
The delivery ducts may be advantageously arranged at least partially in a housing wall in the area of the respective timing case or of the housing section guiding the driving device. By constructing the delivery ducts as cast or bored ducts in the wall of the corresponding housing section, external or internal pipe lines will not be required. The ducts can therefore be produced when the housing is manufactured.
In the crankshaft case, an advantageous housing area for the oil-air separating elements exists approximately in the center of the longitudinal course of the crankshaft, where the constructional gaps between the individual connecting rods may be utilized. In this case, the oil-air separating elements may be advantageously arranged on both sides of the crankshaft, forming a V-shaped or vertical arrangement. This type of construction allows efficient use of the housing space, while permitting a good separating action of air and oil.
These and other objects, features and advantages of the present invention will become more readily apparent from the following detailed description when taken in conjunction with the accompanying drawings.